This invention relates to a nuclear reactor containment vessel and a boiling water nuclear reactor power plant with an enhanced level of safety.
A conventional boiling water reactor (BWR) is referred to as active-safety reactor, when its safety system that includes an emergency core cooling system (ECCS) is formed by using active equipment such as a pump. Meanwhile, a BWR is referred to as passive-safety reactor, when its safety system is formed by using only passive equipment such as tanks, and the cooling water stored in the inside is injected into the reactor by gravity.
An advanced BWR (ABWR) is a typical commercial active-safety reactor. Recently, a reactor concept of partly incorporating a passive-safety system for the purpose of cooling the reactor containment vessel has been studied as a new ABWR, as disclosed in Japanese Patent Application Publication No. 2004-333357.
The soundness of the reactor containment vessels of conventional active-safety BWRs can be threatened when a severe accident is considered to take place to go beyond the design basis. The reactor building surrounding the primary reactor containment vessel is not pressure resistant and is not expected to positively function as an outer containment vessel of a double containment structure by design if the soundness of the primary reactor containment vessel were damaged. If the primary reactor containment vessel is provided with vents for the purpose of maintaining the soundness of the primary reactor containment vessel, radioactive substances could partly be discharged into the environment when such an accident occurred.
On the other hand, conventional passive-safety BWRs are not equipped with an active-safety system by design. Although the system cost of the passive-safety system is low, the pressure in the inside of the primary reactor containment vessel could increase once an accident occurred to damage the reactor core, because of non-existence of counter measure such as provision of vents and the large amount of hydrogen generated in the reactor core.
Additionally, the primary reactor containment vessel could be damaged by hydrogen detonation when an accident occurred because hydrogen would be discharged into the equipment room. When contaminated with radioactivity or if the internal atmosphere of a lower equipment room replaced by hydrogen and an accident occurred, it would be difficult for operators to enter the equipment room for restoration activities. The idea of additionally arranging a steel-made secondary reactor containment vessel as a countermeasure to the above-identified problems and discharging hydrogen into it can provide an enhanced level of safety. However, the addition of such a secondary reactor containment vessel would be costly and cumbersome.
It is desirable that the reactor containment vessel of an advanced BWR of the next generation is highly safe by design so that the internal pressure can be held low, no hydrogen detonation can take place and operators are allowed to enter into the equipment room wherever necessary, even if an accident occurred to the reactor core.
Accordingly, it is an object of the present invention to provide an improved reactor containment vessel that is much safer than any existing ones against assumed severe accidents, and also a boiling water reactor power plant realized by using such a containment vessel.